Bottlehead Forum
Bottlehead Kits => BeePre => Topic started by: debk on April 05, 2013, 02:26:34 PM
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What 300b tubes are you running in your BeePre?
I have tried both the Gold Lion and the Psvane 300b-t. I like the Psvane better. Sounds a little more detailed than the gold lion tube.
Anyone have any other suggestions to try? All the EML 300b seem to have a higher than standard filament current.
Deb
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EML will not work in the amp.
I'm using EH 300B gold grids. They are the only tube I have..... This is an expensive preamp to roll tubes in.
It would be nice to find someone in SoCal with a stash of different 300B's that would be willing to spend some time with the BeePre at my place.
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I thought the EML 300b's would work fine...but the EML 300b-mesh was not recommended. Can you confirm the EML 300b's won't work? I could have sworn that I was told the EML 300b's would be just fine for both the Paramounts and the BeePre.
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The regular EML 300b has a filament current of 1.3A, slightly higher than the 1.25A most 300b are. Don't know if the 1.3A is just 1.25A rounded up or the tube does draw slightly higher filament current than the standard 300b tubes.
I don't know how close the specs are for the filament power supply in the BeePre are, will the extra 50mA make a difference?
Debra
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Admittedly...I guess I'm talking more Paramount than BeePre... but I'm hoping the EML 300b's are fine for either. As for the 50mA question...I'm going to have to defer to someone more knowledgeable.
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There is a thread on it already. Unless you want to put your beePre in a fridge to keep it cool, EML tubes will not work in the BeePre (they work fine in the Paramount). They all draw too much current and with the highly regulated filament supply you will starve the tubes. You could adjust the regulator which PJ says is possible (and the transformer has the reserve) but at the cost of more heat. I asked Jac and he of course said he will not warrenty the tubes if they are not run to proper current.
We should focus on the tubes we can use safely in the BeePre and keep on Bottlehead to add this adjustablility to version 1.1. Or if someone wants to adjust their regulators and spend a good amount of change to try it, please post your results and temp readings of the BeePre. I really want to use EML myself, don't get me wrong but I also want the tubes and the preamp to have a long and happy life.
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The other thread is mainly about the EML mesh plate 300b which has a filament current of 1.5A. That we know will not work
Is there enough reserve for the 1.3A draw of the solid plate EML 300b in an unmodified BeePre?
Deb
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Has anyone tried the Shuguang 300BC solid graphite plates? I have a pair in an Audio Note Meishu integrated, replacements for some low mileage WE 300Bs I'm saving for a rainy day. The Shuguans aren't WEs, but they are better all around then the EH's that came with the amp when I bought it used.
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Not sure how many folks will want to cough up nearly as much for tubes as they pay for our kit. I'm thinking that the best approach might be to offer a separate mod kit that allows changing the circuit to work with the EMLs - which would necessarily make it incompatible with 300Bs.
Perhaps Jac could be persuaded to loan us a pair of tubes to develop the necessary mods with.
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hmm...well... I bought 3 pair of EML 300b's. pfft.
ok...I'm sure it was mentioned previously, but to avoid any further ordering mistakes, exactly which tube should I get for the BeePre? The Psvane 300b-TII's?
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Not sure how many folks will want to cough up nearly as much for tubes as they pay for our kit. I'm thinking that the best approach might be to offer a separate mod kit that allows changing the circuit to work with the EMLs - which would necessarily make it incompatible with 300Bs.
Perhaps Jac could be persuaded to loan us a pair of tubes to develop the necessary mods with.
:) maybe so! Would you guys be willing to send the email to Jac?
If such a kit was to be produced, it would be nice if it could have the resistors and specs to change the regulators along the full range of current draw, from stock 1.2 A to 1.5 A.
I would buy the kit in a heart beat and I bet most current BeePre owners would too. EML tubes are hard to beat if you are willing to pay for them.
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The other thread is mainly about the EML mesh plate 300b which has a filament current of 1.5A. That we know will not work
Is there enough reserve for the 1.3A draw of the solid plate EML 300b in an unmodified BeePre?
Deb
Deb the way I understand it the current is regulated to 1.2 amps, not 1.25 amps. Hopefully PJ will weigh in on the 1.3 amp load.
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A 300B preamp is not a trivial pursuit as can be guessed by the number of them on the market. It turned out to require some pretty unique design elements to work to the sonic standard we require. It's quite a bit different than the traditional 300B amp with AC filaments that most 300Bs are made to work with.We supply the kit with EH 300Bs. We have not tried all of the boutique tubes, so I am hesistant to make any recommendation about other tubes unless they meet the standard WE spec for 300B filament voltage and current. The nature of our regulation scheme is such that it has to be modified for any tubes that don't run at the filament spec of the tube the preamp is designed for - a spec 300B. There is also the potential issue of how microphonic a given tube design might be. Again I can't comment on what I haven't heard. If boutique tube manufacturers would like the opportunity to have us recommend their product and they are willing to send us a pair of tubes to work with we can determine if adjustments to the regulator are necessary and if the level of microphony is acceptable for the application.
As regards EMLs, I will let PJ weigh in on that. He has had some discussion with Jac about the requirements of the EML tubes and I'm not sure if they are compatible with the regulation method we use to get the S/N ratio as good as it is.
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Anyone have any experience with the KR audio 300b?
Deb
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Anyone have any experience with the KR audio 300b?
Deb
Please buy a pair and give us a comparison to your PSvane tubes. I've been on the fence with both pair..
I'm actually really happy with the EH gold grids. Mind you, I have nothing to compare them to......
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Anyone have any experience with the KR audio 300b?
Deb
Please buy a pair and give us a comparison to your PSvane tubes. I've been on the fence with both pair..
I'm actually really happy with the EH gold grids. Mind you, I have nothing to compare them to......
The KR tube spec for the 300b WE clones are as follows:
Maximum Plate Voltage 550 V
Maximum Plate Current 120 mA
Plate Dissipation 50 Watts
Va 450 V
Ia 100 mA
Vg -90 V
Transconductance 6.2 mA/V
Amplification Factor 3.9
Filament Voltage 5 V (DC/AC)
Filament Current 1.2 A
Should I expect these to be acceptable for the BeePre based on the spec?
for comparison...here's the EML 300b specs:
300B Filament Ratings
Filament Voltage 5 Volt (AC or DC)
Tolerance on filament voltage 4%
Filament Current 1.3 Ampere
300B Maximum Conditions Not possible as operating point
Plate Voltage 450Volt
Plate Current 100mA
Power Output in Class A 17.8 Watt
Plate Dissipation 40Watt (note5)
Grid resistor with Auto Bias 250k Ohm (note4)
Grid resistor with Fixed Bias 50k Ohm (note4)
300B Factory Test conditions
Plate Voltage 300V
Plate Dissipation 17Watt
Plate Current 56mA
Grid Voltage -58Volt
Plate Impedance 700 Ohm
Amplification Factor 3,9
Transconductance 5.6 mA/V
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As regards EMLs, I will let PJ weigh in on that. He has had some discussion with Jac about the requirements of the EML tubes and I'm not sure if they are compatible with the regulation method we use to get the S/N ratio as good as it is.
Jac is naturally disappointed that the design is not at present flexible enough to accommodate his tubes - well, so am I! The mesh especially has such a great reputation that I would totally love to hear it.
As I have told Jac, I will continue to pursue a design revision - as Doc B said, we have had to do quite a bit of research and have wound up with a more complex and less flexible circuit than we would prefer. Jac has a lot of analysis, good ideas, and good advice for designers on his web site, as well.
I do have a research plan for this issue. It will have payoffs (hopefully) for several upcoming products, including the BeePre. I won't promise a payoff any faster than the DAC project, now 2 years and counting, though. If you can predict or schedule the outcome, then it isn't research!
Meanwhile, yes the regulator has enough current headroom for 1.3 amps. I've done some calculations that suggest a certain amount of flexibility, but I'm not ready to specify anything except the stock tube until I have an adequate body of actual measurements - there are too many variables that seem small but may or may not add up.
For those who have good meters (1% accuracy or better), you might measure the voltage at the filament pins (1 and 4) of the 300Bs and report them. I'll accumulate the body of data, which will help me validate my analysis and also assess parts and build variability.
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Thanks Paul! I'll get you a measurement tomorrow. If 1.3 Amps turns out to be an option I will take EML solid plates over anything else based on only my great experience with his other tubes.
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I would be curious to hear someone's impression of Valve Art 300Bs in the BeePre. I've enjoyed their EL34 and EL84 tubes in my dynaco amps.
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For those who have good meters (1% accuracy or better), you might measure the voltage at the filament pins (1 and 4) of the 300Bs and report them. I'll accumulate the body of data, which will help me validate my analysis and also assess parts and build variability.
Here are mine:
EH Gold Grid tubes
Line: 120.2
B4: 9.88
B1: 5.04
A4: 9.82
A1: 4.99
edited for poor typing....
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I don't think the line voltage is relevant. Still good for you to see 120v. Mine is so high I can't connect anything directly.
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Thanks, Aaron. I see 0.6% difference in the regulated voltage, 0.6% different and within spec since the voltage-set resistors are 1% parts. The means the voltage loss in the wiring is very small, and the solder joints are good.
The A tube is getting 4.83v, and the B tube is getting 4.44 volts (by subtraction). Both of these might go up as the tube comes to full temperature. You can swap the tubes and see if the difference moves with the tube. If it moves with the tube, then the B tube is drawing more current - 1.36 amps if the 8 ohm resistors are spot on and your measurements are exact. If it doesn't move with the tube, then either the 8 ohm resistors are off a bit (they are supposed to be 1% parts) or there's a questionable connection. Most meters can't measure low resistances with sufficiently reliable accuracy so I don't suggest making that measurement.
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Thanks Paul. This was with only a minute or two of warm up. B tube was slowly drifting down as it warmed up. I will try it again tomorrow and repost the results. I didn't use stock resistors but Mills 8 Ohm 1% parts. That doesn't mean they are not off though.
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Hard to go wrong with Mills; good choice. I'm quite interested in any measurements, since we have very little experience with this "in the field" as yet. I was startled at the high current/low voltage at first, but as I thought about it I realized that the filament doesn't come up to full temperature until the plate has had enough time to radiate its heat to the filament - and the filament resistance increases with temperature.
I plan to be at BottleHeadquarters next week, and will try to get some data on Doc B's preamp.
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Is there a specified amount of warm up time you would like us to have before making measurements so as to not introduce any other variables into the data?
I'll try to get data on mine this weekend.
Deb
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Today's data with 20 mintues of warm up:
EH Gold Grid tubes
B4: 9.88
B1: 5.02
A4: 9.82
A1: 4.98
After reviewing my notes from yesterday I messed up on the B1 voltage. The previous thread has been edited. There is very little difference from the intial results after a couple of minutes and at the 20 minute mark.
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At 5 minutes everything should be settled out. Then listen for half an hour. See if the measurements moved. I doubt they will move by as much as 2%.
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Thanks, Aaron - good data. The tubes seem to be getting 4.84-4.86 volts which is 3% low, well within the usual +/-10% and the more strict +/-5% that premium tubes often specify.
EML specifies +/-4%. For a quick estimate, let's assume your Mills resistors are exact and that your meter is also exact. Then averaging the two tubes, your actual current would be 5.00v/4 ohms, or 1.25 amps. If you increased to 1.3 amps, the resistor drop would be 5.2 volts, leaving 9.85-5.2=4.65 volts which is 7% low - below the EML spec.
As you can calculate, a 56 ohm resistor in parallel with the two 8-ohm resistors would, in this case, give 5.00 volts on the 300B filament. I am not recommending this, at least not yet, and I won't be making any recommendations until we have a greater variety of data on the variability from one build to another. But you can see where I'm headed. I expect this will prove to be better than adjusting the regulated voltage, which is a delicate balance between the available voltage and the heat wasted in the regulator.
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Thanks Paul. I'm all ears as this continues to develop. Thank you for giving your time to this pursuit.
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I just got a pair of KR 300b and am listening to them now. Compared to the Psvane the KR's sound a little more open/spacious and more accurate. The bass is about the same, but the highs are more clear. I prefer them to the Psvane.
The only drawback is that the top is a little wider than the Psvane so the lead damper rings don't fit as well.
I am very glad I spent the money to get them. They are on sale at TubeDepot for $599 a pair
Debra
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Thanks Deb! I'm very tempted by those tubes. Too bad we don't live closer together so I could listen to your stash!
When you get a chance, could you post the current draws for your different tubes? It would be interesting to see what the KR tubes draw..
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I have about 5 hours on the KR's now. They have "opened" up more, very spacious and detailed sounding. I am very happy I bought these, the best sounding 300b I have tried in the BeePre.
The data sheet that came with the tubes say the filament current is rated at 1.2A. The actual test data included with the tubes are 1.11A and 1.12A.
I have not had a chance to make any measurements myself. When I get a chance I will drag it down to Lab (Ok, Basement but Lab sounds better) and make some measurements
Deb
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Thanks Deb, though it raises more questions and concerns.
PJ, Deb's tubes are drawing less that normal WE spec current. I called the TubeDepot and all of their tubes in stock draw 1.13 amps or less. Thoughts??
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... all of their tubes in stock draw 1.13 amps or less. Thoughts??
So, they don't meet their spec, do they? But it's close. When I have more voltage data, I'll have some thoughts....
The voltage variation is about half the current variation, so 1.13amps is 6% low and the voltage would be 3% high, close enough. Do the numbers, and you'll see that 1.1 to 1.3 amps is a nominally safe range - if we ignore variations in component values and build resistances in individual amps. So I am looking to learn what the build variations may be, and what the tube variations may be, before making any recommendations.
Ignoring the other variations as above, you might think you could say that a 1.3A tube will work. But you can't say a tube model with 1.3A +/-0.5A current draw will work - half of them will draw too much current.
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Without more data I wouldn't want to try the 1.3A EML.
Though the KR don't quite meet spec they sound very good.
I will try and get you voltage data next week. My son is coming for a visit this weekend and I probably will not get to it till next week
Deb
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One other observation about the KR tubes, they are much less microphonic than the Psvane are.
Deb
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I tried the TJ 300B mesh this weekend. I enjoyed this tube in my Paramounts but it wasn't the best combo for my BeePre and speakers. Too light weight, no body or soul. I only gave them an hour or so but to my ears and system, the EH 300B Gold Grid have been the best sounding tube so far.